Question

If p → q is true, then ~ p → ~ q is __________ true.

always
sometimes
never

Answer 1

Let p be the statement that
x = y
and let q be the statement that
x+1 = y+1

Then it is clearly the case that
p → q

But what about
~ p → ~ q
?
Well, that statement is false in this case. Hence it can NOT be that
p → q ALWAYS implies ~ p → ~ q

But are there cases when
p → q does implies ~ p → ~ q
?

Answer 2

Yes there are. Let p and q be the same statement. Then p → q, because p → p.
And that does imply that ~p → ~q because ~p → ~p

Therefore, what's the answer to your question?